Enhanced Methanol Oxidation Activity Research Articles

Enhanced methanol oxidation activity of porous layered Ni/CeO2@CN nanocomposites in alkaline medium

The performance of direct methanol fuel cells (DMFC) partly depends on the development of economical and efficient methanol oxidation catalyst. Here, porous layered Ni/CeO2@CN-T composites were prepared by complexation and pyrolysis two-step methods. The optimal Ni/CeO2@CN-600 for methanol oxidation reaction (MOR) requires only 1.361 V at the current density (j) of 10 mA cm−2, and the j is as high as 229.56 mA cm−2 at 1.642 V, superior to those of the nickel-based catalysts reported. The excellent properties of Ni/CeO2@CN-600 are mainly attributed to the electronic interaction between Ni and CeO2, the uniform dispersion of Ni and CeO2 nanoparticles and its porous layered structure. Meanwhile, it has better stability after 12 h i-t tests. The CO poisoning experiments showed that the anti-CO poisoning ability of Ni/CeO2@CN-600 was obviously stronger than that of Pt/C catalyst in alkaline medium. Finally, the density functional theory (DFT) calculation shows the superior activity of Ni/CeO2 catalysts for MOR is mainly attributed to the higher adsorption energy of Ni/CeO2 for CH3OH and the lower energy barrier.

Platinum doped titanium dioxide nanocomposite an efficient platform as anode material for methanol oxidation

TiO2@Pt nanocomposite was synthesized using a simple one-step coprecipitation method as an electrocatalyst for methanol oxidation. Pt nanoparticles were supported by using TiO2 as a support material, thereby providing strong metal-support interactions. The TiO2@Pt nanocomposite characterized by Field Emission Scanning Electron Microscope (FESEM) and Energy Dispersive X-ray analysis (EDX) revealed the spherical shape of TiO2 crystalline matrix with finely dispersed Pt nanoparticles. In the powder X-ray diffraction (XRD) analysis, the diffraction peaks observed for the TiO2 and TiO2@Pt nanocomposites were composed of mixed phases of anatase and rutile. Electrochemical performances are evaluated in an aqueous 0.1 M KOH electrolyte and 0.1 M CH3OH as a target analyte. The Pt@TiO2 nanocomposite showed high electrocatalytic activity towards methanol oxidation, the results indicated that the bare Pt electrode has catalyzed the oxidation of methanol with a strongly weak oxidation peak (J = 0.25 mA/cm2), while TiO2 modified Pt electrode which showed higher catalytic activity towards methanol oxidation with a current density of 0.48 mA/cm2. The methanol oxidation was increased compared to a commercially available Pt/C reference catalyst, as shown by a shifted methanol oxidation peak potential and an increased peak current density. As demonstrated by cyclic voltammetry, these increased activities have been clarified by enhanced methanol oxidation activities. An enhanced methanol oxidation activity is attributed to the metal support interaction due to TiO2 nanoparticles, therefore resulting in a weak CO chemisorption on the surface of Pt. Finally, with such valuable features of electrochemical sensitivity and great catalytic activity, the synthesized TiO2@Pt-3 nanocomposite is used as the anode material for methanol fuel cell application.

Enhanced Methanol Oxidation Activity of PtRu/C100−xMWCNTsx (x = 0–100 wt.%) by Controlling the Composition of C-MWCNTs Support

PtRu nanoparticles decorated on carbon-based supports are of great interest for direct methanol fuel cells (DMFCs). In this study, PtRu alloy nanoparticles decorated on carbon Vulcan XC-72 (C), multi-walled carbon nanotubes (MWCNTs), and C-MWCNTs composite supports were synthesized by co-reduction method. As a result, PtRu nanoparticles obtained a small mean size (dmean = 1.8–3.8 nm) with a size distribution of 1–7 nm. We found that PtRu/C60MWCNTs40 possesses not only high methanol oxidation activity, but also excellent carbonaceous species tolerance ability, suggesting that C-MWCNTs composite support is better than either C or MWCNTs support. Furthermore, detailed investigation on PtRu/C100−xMWCNTsx (x = 10–50 wt.%) shows that the current density (Jf), catalyst tolerance ratio (Jf/Jr), and electron transfer resistance (Ret) are strongly affected by C-MWCNTs composition. The highest Jf is obtained for PtRu/C70MWCNTs30, which is considered as an optimal electrocatalyst. Meanwhile, both PtRu/C70MWCNTs30 and PtRu/C60MWCNTs40 exhibit a low Ret of 5.31–6.37 Ω·cm2. It is found that C-MWCNTs composite support is better than either C or MWCNTs support in terms of simultaneously achieving the enhanced methanol oxidation activity and good carbonaceous species tolerance.

Specific Metal–Support Interactions between Nanoparticle Layers for Catalysts with Enhanced Methanol Oxidation Activity

Oxide supports often play a critical role in metal-supported catalysts owing to their charge transfer phenomena that can alter catalytic performance. Herein, in place of conventional bulk oxide supports, monodisperse oxide nanoparticles (NPs) were exploited as supports for Pt catalysts. Depending on the type of oxide NP, Pt/oxide layered catalysts exhibited dramatic changes in the catalytic activity and selectivity for methanol oxidation. While Pt NPs deposited on MnO, Fe3O4, Co3O4, Cu2O, and ZnO NPs had comparable turnover frequencies to that of the pure Pt NP catalyst, Pt deposited TiO2 NPs changed the reaction rate significantly, with preferential selectivity observed toward partial oxidation products. Facet-specific interactions between Pt and TiO2 NPs were demonstrated by density functional theory calculations and catalytic reactions using shape-controlled TiO2 NPs. When Pt NPs were attached to spherical and rhombic TiO2 NPs with abundant (001) surfaces, methanol conversion was enhanced 10-fold owing to strong charge transfer from TiO2 to Pt.

Unique Cu@CuPt Core–Shell Concave Octahedron with Enhanced Methanol Oxidation Activity

Although tremendous efforts have been devoted to the exploration of cost-effective, active, and stable electrochemical catalysts, only few significant breakthroughs have been achieved up to now. Therefore, exploring new catalysts and improving catalyst activity and stability are still major tasks at present. Controllable synthesis of Pt-based alloy nanocrystals with a uniform high-index surface and unique architecture has been regarded as an effective strategy to optimize their catalytic efficiency toward electrochemical reactions. Accordingly, here we present a one-pot facile solvothermal process to synthesize novel unique Cu@CuPt core-shell concave octahedron nanocrystals that exhibit both outstanding activity and long durability. By regulating temperatures during the synthesis process, we were able to control the reduction rate of Cu and Pt ions, which could subsequently lead to the sequential stacking of Cu and Pt atoms. Owing to the concave structure, the as-prepared core-shell nanoparticles hold a high-index surface of {312} and {413}. Such surfaces can provide a high density of atomic steps and terraces, which is suggested to be favorable for electrochemical catalysts. Specifically, the Cu@CuPt core-shell concave octahedron presents 8.6/13.1 times enhanced specific/mass activities toward the methanol oxidation reaction in comparison to those of a commercial Pt/C catalyst, respectively. Meanwhile, the as-prepared catalyst exhibits superior durability and antiaggregation properties under harsh electrochemical conditions. The facile method used here proposes a novel idea to the fabrication of nanocrystals with desired compositional distribution, and the as-prepared product offers exciting opportunities to be applied in direct methanol fuel cells.

Enhanced methanol oxidation activity and stability of Pt particles anchored on carbon-doped TiO2 nanocoating support

In this work, carbon-doped TiO2 nanocoating (TiO2–C) was prepared by a sol–gel process and employed as the support of Pt nanoparticles for methanol oxidation reaction (MOR). The obtained Pt/TiO2–C catalyst was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. XRD characterization shows that the average crystallite sizes of Pt particles and TiO2–C support are 2.7 and 6.5 nm, respectively. TEM characterizations show that Pt particles are highly dispersed on TiO2 nanocoating, which preserves its nanoscale structure without no apparent sintering after carbon doping. XPS characterization shows that the Pt particles anchored on TiO2–C exhibit positively shifted binding energies of Pt 4f. Cyclic voltammetry (CV) and chronoamperometry (CA) characterizations show that TiO2–C has a greatly enhanced electrical conductivity and Pt/TiO2–C catalyst has better electrocatalytic activity and stability than Pt/C catalyst for MOR, which could be attributed to the high dispersion of Pt particles on TiO2–C support, the strong metal-support interactions between Pt particles and TiO2–C support, and the rich active –OH species on TiO2–C support.

Enhanced methanol oxidation activity of Au@Pd nanoparticles supported on MWCNTs functionalized by MB under ultraviolet irradiation

A successful approach to assemble Au core Pd shell (Au@Pd) nanoparticles on the surface of multi-walled carbon nanotubes functionalized by methylene blue (MB) (Au@Pd/fuv-MWCNTs) was reported. In this method, MWCNTs were functionalized under ultraviolet irradiation. UV–Vis analysis and high-angle annular dark-field transmission electron microscope (HAADF-TEM) image prove that core–shell structure of Au@Pd nanoparticles forms. TEM results indicate that Au@Pd nanoparticles (~5.2 nm) are well-dispersed on the surface of fuv-MWCNTs. X-ray photoelectron spectroscopy (XPS) reveals that ultraviolet irradiation can promote the interaction between Au@Pd nanoparticles and the functional groups on the surface of MWCNTs. Cyclic voltammograms (CV), chronoamperograms (CA), and electrochemical impedance spectroscopy (EIS) results demonstrate that the Au@Pd/fuv-MWCNTs catalysts show excellent electrocatalytic performance for methanol oxidation in alkaline media. The catalytic activity of the Au@Pd/fuv-MWCNTs is ~2 times higher than that of the commercial Pd/C catalysts. This is mostly attributed to that ultraviolet irradiation can make the moieties of MB provide a uniform surface with active and anchoring sites, and improves the functional effect of MB on the surface of MWCNTs. Especially, ultraviolet irradiation modifies electronic structure of Pd and is beneficial for the enhancement of catalytic activity.

Highly Stable Pt–Au@Ru/C Catalyst Nanoparticles for Methanol Electro-oxidation

Among the major obstacles to the successful application of Pt–Ru alloys as anode electrocatalysts for direct methanol fuel cells are their low electrocatalytic activities and poor stability under demanding operating conditions. In particular, detrimental is the eventual dissolution of the more oxophilic Ru. In this work, a novel carbon-supported gold-stabilized Pt–Au@Ru catalyst was synthesized using the water-in-oil microemulsion method. The catalyst possesses an enhanced methanol oxidation activity in acid medium and significantly enhanced stability over a commercially available Pt–Ru/C catalyst (E-TEK, 60%). This work provides a representative example of stabilization of an oxophilic transition element, Ru, using a unique ternary structure with Au. The stabilized surface and bulk composition are determined through copper under-potential deposition, transmission electron microscopy, X-ray diffractometry, and X-ray photoelectron spectroscopy in conjunction with electrochemical measurements. In situ X-ray...

Controlled Synthesis of PtRu/Graphene Nanocatalysts with Enhanced Methanol Oxidation Activity for Fuel Cells

Weigh the anchor! PtRu/graphene nanocatalysts with tunable and excellent electrochemical performance for methanol oxidation can be prepared through uniformly anchoring PtRu nanoparticles with small sizes onto graphene sheets through a simple one-step reduction method without surfactant. The graphene sheets are a promising support to optimize the electrocatalytic activity of fuel cells.

Enhanced methanol oxidation activity of Pt catalyst supported on the phosphorus-doped multiwalled carbon nanotubes in alkaline medium

Abstract Phosphorus-doped multiwalled carbon nanotubes (P-MCNTs) were synthesized by thermolysis and employed as the supports of platinum catalyst. It was found that Pt/P-MCNTs as an anode catalyst exhibited a much higher activity and better stability toward methanol electrooxidation than the Pt/MCNTs without phosphorus in alkaline medium, due to the higher Pt utilization ratio and Pt area-specific activity, the better electronic conductivity of P-MCNT support and the faster rate of charge transfer at the P-MCNTs/electrolyte interface, indicating a highly potential application of Pt/P-MCNTs as anode catalyst for methanol oxidation in alkaline DMFC.

Nano-boron carbide supported platinum catalysts with much enhanced methanol oxidation activity and CO tolerance

Platinum (Pt) nanoparticles were successfully deposited on the surface of nano-B4C with fragmentary nanostructured carbon thin film through a polyol process in an ethylene glycol solution. The electrochemical surface area of the Pt/B4C was investigated and showed remarkable enhancement compared with conventional Pt/C catalysts, which could be attributed to fast hydroxyl adsorption and high OHad coverage occurring during the hydrogen desorption process. It was also found that the novel Pt/B4C catalysts presented much enhanced methanol oxidation activity and CO tolerance by a negative shift in the onset potential and an increase of the peak current density in comparison to Pt/C catalysts. Meanwhile, the Pt/B4C showed an improved oxygen reduction reaction activity compared to the Pt/C catalyst.

FePt concave nanocubes with enhanced methanol oxidation activity

FePt concave nanocubes enclosed by highly active high-index atom steps were synthesized by a facile process. The oleic acid was demonstrated to be the key point for the formation of FePt concave nanocubes. Due to the concave structure, the FePt concave nanocubes exhibit higher electrocatalytic activity than either FePt nanocubes or commercial Pt catalysts in methanol oxidation.

Formation of PtRu alloy nanoparticle catalyst by radiolytic process assisted by addition of dl-tartaric acid and its enhanced methanol oxidation activity

PtRu nanoparticle catalysts with 2-nm size supported on carbon were synthesized by a radiolytic process, assisted with the addition of dl-tartaric acid. Gradual alloying with the addition was confirmed by structural analyses with techniques of the X-ray diffraction and the X-ray absorption fine structure. Their methanol oxidation activities evaluated by the linear sweep voltammetry were higher than that of the commercial one, and found to be enhanced in accordance with the gradual change in the bimetallic structure from the Pt-core/Ru-shell to the random alloy. A good correlation was found between the catalytic activity and the indicators, which stands for the occurring frequency of the Pt–Ru bonds, calculated from the coordination numbers determined by the extended X-ray absorption fine structure analysis. It was confirmed that the addition of dl-tartaric acid in the radiolytic process certainly promoted the random alloy formation of PtRu bimetallic nanoparticles and enhanced their methanol oxidation activity.

High Methanol Oxidation Activity of Well-Dispersed Pt Nanoparticles on Carbon Nanotubes Using Nitrogen Doping

Pt nanoparticles (NPs) with the average size of 3.14 nm well dispersed on N-doped carbon nanotubes (CNTs) without any pretreatment have been demonstrated. Structural properties show the characteristic N bonding within CNTs, which provide the good support for uniform distribution of Pt NPs. In electrochemical characteristics, N-doped CNTs covered with Pt NPs show superior current density due to the fact that the so-called N incorporation could give rise to the formation of preferential sites within CNTs accompanied by the low interfacial energy for immobilizing Pt NPs. Therefore, the substantially enhanced methanol oxidation activity performed by N-incorporation technique is highly promising in energy-generation applications.